When spinning a plurality of different specimens in a centrifuge, it is critical that the weights of the specimens be approximately equalized to avoid the creation of unbalanced tangential (centrifugal) forces, which prevent smooth operation of the centrifuge a which may damage its bearings or even result in an "explosion". Similarly, the specimen must be placed approximately equidistant from each other around the circumference of the centrifuge plate.
Larger laboratory centrifuges such as those used in blood banks for component preparation usually have four or six cups arranged on pivots all located in a single plane perpendicular to and passing through the central axis of the centrifuge, each pivot itself being perpendicular to the central axis. To facilitate the handling of the specimens, cup inserts are provided. These inserts are of uniform configuration and weight, and specimens are generally placed into a cup insert and the specimen and insert then placed in the cup.
Where a variable amount of specimen is available or may be centrifuged, balancing of the cups is achieved very simply by using identical aliquots. However, this is not possible where fixed amounts of different specimens are to be centrifuged or where the different specimens have differing masses, or where the specimens are each in sealed containers, such as whole blood.
The centrifuging of whole blood, which is exemplary of this invention but not limiting, has produced certain laboratory practices which best illustrate the problem.
In centrifuging whole blood during blood component preparation, each donor's blood sample is kept in a separate bag during processing. This is to permit separate recovery of different types of blood products, to maintain sterility, and to prevent contamination of other donor's blood by a sample containing, for example, hepatitis virus.
The whole blood is kept in the same flexible, sealed plastic bag into which it is first removed from the donor. The bags, each containing a donor's specimen, are placed into conventional cup inserts and the combination is weighed. Since the amount of specimen will vary somewhat from bag to bag, in some laboratories and blood banks small additional weights are added to the cups until a uniform weight is achieved for all the cup insert-specimen bag combinations. This is achieved, in practice, by setting a weight somewhat higher than that expected for any given bag-cup combination, weighing each bag-cup separately, and adding rubber bands, rubber or plastic chips, etc., to each cup insert until the desired combined weight is achieved.
Water, or some other neutral liquid, would normally be an ideal weight-adjusting substance, since it is freely available and almost infinitely variable in weight. However, liquids are not suitable in many instances. In the case of blood bags, each bag is labelled with at least a coded label which identifies the donor, and which must not be destroyed. Water may adversely affect the legibility of parts of the coded label.
No prior art is known to the inventor which closely relates to this invention. However, the following U.S. patents are of some interest.
U.S. Pat. No. 3,851,817 discloses double walled containers for use in a centrifuge containing a liquid between the walls. However, the disclosure does not vary the amount of liquid, which is permanently sealed within the container (column 1, line 68 to column 2, line 1). The purpose of the container is for cooling blood samples, and there is no disclosure of its use for balancing. In fact, since the liquid is sealed within the container, it could not be used for the purposes of this invention.
U.S. Pat. No. 2,351,708 relates to a method of protecting glass containers and the like during centrifuging. FIG. 3 discloses a double-walled cup (container) with fluid between the walls, and the top may optionally be open (unsealed) as per page 2, right-hand column, line 15. FIG. 4 appears structurally similar to the subject invention, but only at first glance and it is noted that liquid is placed between the centrifuge receiver and the cup, separated by elastic washers. The fluid levels may be adjusted (page 2, right-hand column, line 35) but no mention is made of the use of the device to adjust the weight or balance.
U.S. Pat. No. 2,526,165 discloses double-walled containers in which a cooling liquid is placed between the walls. The liquid is sealed between the walls (column 1, line 29; column 2, lines 18-27) and the compartment is substantially filled (column 2, line 14; column 2, line 40). Thus, although the devices appear structurally related, they cannot be utilized for the purposes of the present invention.
U.S. Pat. No. 3,921,898 is of lesser interest in that it discloses a device for balancing all of the containers in a centrifuge by providing a connecting conduit with a liquid reservoir for each receiver. The balancing is automatic and is effected only when the centrifuge is operated.